This invention relates to a bag-making machine and more particularly relates to an improved sealing-cutting mechanism in a machine for fabricating bags from thermoplastic material of tubular, flexible stock.
U.S. Pat. No. 3,801,409 issued Apr. 2, 1974 discloses a method and apparatus for forming bags from tubular feed stock of thermoplastic material such as polyethylene or polypropylene by heat and pressure sealing together the opposed sides of a flattened tube of said stock to form a bag bottom while substantially concurrently cutting said stock adjacent the seal for severing the preceding bag from the stock. Each newly formed bag must then be discharged from the bag-making machine and the stock advanced to the desired at-rest position for the next sealing-cutting operation.
This method described in the foregoing patent is directed to the sealing of the open end of tubular stock material and first discharging the resulting closed end from the machine. A desired length of the stock is then severed and the newly formed bag transported a short distance to a stacking bin by simple stacking wheels while the severed end of the stock material is concurrently heat-sealed for a repeat of the bag-making cycle.
A knife having a serrated cutting edge and adapted to reciprocate into and out of a mating recess disposed transversely of the direction of travel of the stock material normally is used to sever the newly formed bag prior to removal of the bag to a stacking bin. The knife edge must be maintained sharp and dulling of the components which make up the cutting edge can result in tearing of the bag material with shut-down of the bag-making process. Also, residue or torn material can jam the knife resulting in the cutting edge being deflected and broken with resulting machine shut-down.
It is an important object of the present invention to provide an improved method and apparatus for severing thermoplastic stock material which obviates the need for a sharp serrated cutting edge.